Pullback stirring head for heavy-load friction stir welding

The invention particularly relates to a heavy-load friction stir welding pumpback stirring head which is installed at the front end of a heavy-load friction stir welding main shaft with a stirring needle pumpback function and comprises a stirring needle and a shaft shoulder which are of a split structure, and the head portion of the stirring needle is a spherical section with a conical surface thread. The heavy-load stirring friction welding main shaft with the stirring needle withdrawing function controls the stirring needle to do linear withdrawing motion towards the interior of the shaft shoulder in the state that the stirring needle and the shaft shoulder synchronously rotate. According to the pumpback stirring head for heavy-load friction stir welding, the design of a large-torque transmission structure for friction stir welding is achieved, the pumpback stirring head is installed and matched with a heavy-load friction stir welding main shaft with a stirring needle pumpback function, and a welding circul